Multi-scale computer-aided design and photo-controlled macromolecular synthesis boosting uranium harvesting from seawater

By integrating multi-scale computational simulation with photo-regulated macromolecular synthesis, this study presents a new paradigm for smart design while customizing polymeric adsorbents for uranium harvesting from seawater. A dissipative particle dynamics (DPD) approach, combined with a molecular dynamics (MD) study, is performed to simulate the conformational dynamics and adsorption process of a model uranium grabber, i.e., PAOm-b-PPEGMAn, suggesting that the maximum adsorption capacity with atomic economy can be achieved with a preferred block ratio of 0.18. The designed polymers are synthesized using the PET-RAFT polymerization in a microfluidic platform, exhibiting a record high adsorption capacity of uranium (11.4 ± 1.2 mg/g) in real seawater within 28 days. This study offers an integrated perspective to quantitatively assess adsorption phenomena of polymers, bridging metal-ligand interactions at the molecular level with their spatial conformations at the mesoscopic level. The established protocol is generally adaptable for target-oriented development of more advanced polymers for broadened applications.


Derivation S1
As shown in Figure S1a, the polymer chain looked like a string, so the center of gravity of the molecule is at the middle side of the chain, and the polymer conformation is completely symmetrical, so we can get equation S1: Under this condition, all of the binding sites are accessible to the uranyl ions.
Supposing that the accessible functional groups coordinate to uranyl ions according to a 2:1 molar ratio, a classical coordination mode between AO ligands and uranyl carbonates in seawater, the maximum theoretical adsorption capacity ( max ) can be obtained as: where i is the mass of the i th part of monomer; i is the distance between the center of gravity of the i th part of monomer and the center of gravity of the whole polymer chain; is the degree of polymerization; is the hydrodynamic diameter of single monomer.

Derivation S2
As shown in Figure S1b, when the polymer chain was completely folded with a fully condensed conformation. To simplify the calculation, a monomer unit is considered to a cube with a length equal to L, and a big cube with the same size as the hydrodynamic diameter of the polymer chain to was employed to substitute the sphere during the following derivation. We can get the side length ( ) of this cube, = √ 3 , and the center of gravity of the polymer chain at the body center of the cube. So, the following equation was obtained to express the g 2 : And the binding sites can be calculated by the specific surface area: For the sphere which has the same volume as the cube, the radius ( ) can be calculated as: So, we can get the ratio between specific surface area of the sphere and that of the big cube: Bring equation S6 into equation S4, we can get the amounts of binding sites:

Electrospinning of the BCPs
The BCPs were dissolved in DMF to prepare electrospinning solutions (12 wt.% in DMF) for spinning on an electrospinner (ET-2535H, Beijing Ucalery Technology Development Co., Ltd). A high voltage of 13.5 kV was adopted and the distance between the needle and drum collector was fixed at 20 cm. The diameter of the using needle is 0.51 mm and the flow rate of the solution is 0.52 mL h -1 with a constant rotational speed of drum collector at 80 rpm.

Amidoximation reaction of nanofiber membranes
The electrospun nanofiber membranes were treated with 10 wt.% hydroxylamine hydrochloride in 50/50 (w/w) water/methanol at 60 ℃ for 4 hours to transform the CN groups into AO groups. The amidoximated membranes were then washed with deionized water 3 times and allowed to dry at 40℃ in an oven overnight.

Adsorption tests in uranium-spiked water
Batch adsorption tests of the electrospun nanofiber membranes were first performed in uranium-spiked water. First, 20 μL of uranyl nitrate aqueous solution (

Uranium enrichment in real seawater and elution
A flow-through system was established to evaluate the uranium enrichment ability of the BCP adsorbents in real seawater. Natural seawater was collected from coastal water near the Boundary Island of South China Sea, with an average uranium concentration of 3.3 ± 0.3 ppb. Before delivering to the test system, the seawater was pumped and filtered through a microfiltration membrane (0.22 μm ) for removing sediments and microorganisms. The polymeric adsorbent membrane was clamped by two pieces of Basotect melamine resin foam and fixed in the center of a column. All parts that may contact with seawater in this system were made of non-metal materials to avoid metal ions contamination. The flow rate of the seawater was controlled to be 200 mL/min and the adsorption lasted for 4 weeks. The adsorption capacity of the adsorbents in were analyzed by ICP-MS. After adsorption, the enriched uranium was eluted with 30 mL HCl solution (0.5 mol/L, 10 minutes, room temperature) and the membrane was then regenerated in 20 mL NaOH solution (5 mmol/L, 5 minutes, room temperature).

Characterizations
The molecular weight (Mn) and molecular weight distribution (Đ)    represent the top and bottom wall beads, 5 represents water, 6 represents PEGMA, 7 represents the active PAO, and 8 represents the dormant PAO.
Supplementary Table 3. The parameters of ij used in the computational study. represent the top and bottom wall beads, 5 represents water, 6 represents PEGMA, 7 represents the active PAO, and 8 represents the dormant PAO.